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15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?
- a)less than 11.33 kN/m3
- b)greater than 11.33 kN/m3
- c)less than 21.33 kN/m3
- d)greater than 21.33 kN/m3
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
15 metres of thick saturated clay is underlain by the sand layer and t...
At C - C
∑ FB = 0
(15 - 12.70) × γsat - 5 × 9.81 = 0
γsat = 21.33 kN/m3
Most Upvoted Answer
15 metres of thick saturated clay is underlain by the sand layer and t...
Understanding the Problem
The scenario involves a 15-meter thick saturated clay layer underlain by a sand layer, which is under artesian pressure equivalent to 5 meters of water head. Excavation is performed up to 12.7 meters in the clay, leading to bottom heave.
Key Concepts
- Saturated Unit Weight of Clay: This refers to the weight of the clay when fully saturated with water.
- Artesian Pressure: The pressure within the sand layer generates a force that can cause heaving when the weight of the overlying soil is insufficient to counteract it.
Calculating Heave Condition
When excavation occurs, the effective stress at the base of the excavation decreases, which can lead to heaving if the upward pressure from the artesian water exceeds the weight of the clay above.
Weight of Water
- The pressure from the artesian water is equivalent to a 5-meter height of water, resulting in a pressure of approximately 50 kN/m² (using the unit weight of water as 10 kN/m³).
Effective Stress Consideration
- The effective stress at the bottom of the excavation can be calculated as:
Effective Stress = Weight of Clay - Artesian Pressure
- For the bottom to remain stable (not heave), the weight of the clay (in terms of unit weight) must be greater than the upward pressure from artesian water.
Unit Weight Threshold
- To prevent heave, the unit weight of the saturated clay must be greater than the upward pressure due to artesian conditions.
- Since the pressure from the 5-meter water head is approximately 50 kN/m², the unit weight of the clay must be sufficiently high to maintain stability.
Conclusion
Therefore, the saturated unit weight of the clay must be greater than 21.33 kN/m³ to ensure that the bottom does not heave during excavation.
Thus, the correct answer is option 'D': greater than 21.33 kN/m³.
The scenario involves a 15-meter thick saturated clay layer underlain by a sand layer, which is under artesian pressure equivalent to 5 meters of water head. Excavation is performed up to 12.7 meters in the clay, leading to bottom heave.
Key Concepts
- Saturated Unit Weight of Clay: This refers to the weight of the clay when fully saturated with water.
- Artesian Pressure: The pressure within the sand layer generates a force that can cause heaving when the weight of the overlying soil is insufficient to counteract it.
Calculating Heave Condition
When excavation occurs, the effective stress at the base of the excavation decreases, which can lead to heaving if the upward pressure from the artesian water exceeds the weight of the clay above.
Weight of Water
- The pressure from the artesian water is equivalent to a 5-meter height of water, resulting in a pressure of approximately 50 kN/m² (using the unit weight of water as 10 kN/m³).
Effective Stress Consideration
- The effective stress at the bottom of the excavation can be calculated as:
Effective Stress = Weight of Clay - Artesian Pressure
- For the bottom to remain stable (not heave), the weight of the clay (in terms of unit weight) must be greater than the upward pressure from artesian water.
Unit Weight Threshold
- To prevent heave, the unit weight of the saturated clay must be greater than the upward pressure due to artesian conditions.
- Since the pressure from the 5-meter water head is approximately 50 kN/m², the unit weight of the clay must be sufficiently high to maintain stability.
Conclusion
Therefore, the saturated unit weight of the clay must be greater than 21.33 kN/m³ to ensure that the bottom does not heave during excavation.
Thus, the correct answer is option 'D': greater than 21.33 kN/m³.
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15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? for Civil Engineering (CE) 2025 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer?.
15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? for Civil Engineering (CE) 2025 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer?.
Solutions for 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? in English & in Hindi are available as part of our courses for Civil Engineering (CE).
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15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer?, a detailed solution for 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? has been provided alongside types of 15 metres of thick saturated clay is underlain by the sand layer and the sand layer is under artesian pressure equivalent to 5 metres head of water. Excavation is started and is it done up to 12.7 metres of depth in the clay layer at which the bottom heaves. For this much excavation depth in the clay. How much-saturated unit weight of clay you expect such that bottom will not heaves?a)less than 11.33 kN/m3b)greater than 11.33 kN/m3c)less than 21.33 kN/m3d)greater than 21.33 kN/m3Correct answer is option 'D'. Can you explain this answer? theory, EduRev gives you an
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